1. Field of Invention
This invention relates to an electronic circuit means for automatically electronically disconnecting a subscriber's telephone line signal receiving and transmitting terminal equipment from a subscriber's end of a telephone loop circuit when a second telephone set or other terminal equipment is taken off-hook when the line signal receiving and transmitting terminal equipment is operating in an off-hook mode.
2. Prior Art
In telephone systems, a two wire loop is provided between a central office and subscriber's telephonic signal receiving and transmitting terminal equipment. A direct current (DC) voltage within the approximate range of from 42.5 volts to 52.5 volts is applied to the loop circuit as a signal carrier voltage at a central office and this is referred to as a central office battery. The central office has a means for superimposing an additional alternating current (AC) bell ringing voltage on the signal carrier voltage for notifying the subscriber of an incoming call. The bell ringing voltage is nominally between seventy-five and one hundred twenty volts and is primarily for actuating telephone bells on the subscriber's terminal equipment. This bell ringing voltage has been employed in telephone answering equipment for actuating the answering equipment and placing it in an off-hook mode. When the answering equipment goes off-hook, a switch in the answering equipment is closed permitting the signal carrier current to flow around the loop, thereby allowing the answering equipment to perform its function to transmitt and receive telephone signals. This terminal equipment to which the present invention is applicable includes telephone sets, telephone answering machines, computer terminal telephonic equipment, and similarly functioning equipment designed to be actuated by an incoming telephone signal and respond thereto over the telephone loop circuit.
When a telephone answering machine is hooked into the telephone loop circuit and is turned on to be operable, each time an incoming bell signal voltage actuates it, the machine goes off-hook and sends and receives messages in a pre-programmed manner. If a subscriber wishes to intercept any message using a telephone set on the same subscriber's loop circuit, the subscriber must first turn the answering machine off or it will continue to send its pre-recorded message and continue to function in the pre-programmed manner interfering with the subscriber's use of the telephone set. This invention provides a means for automatically disconnecting the answering machine or other terminal equipment in an off-hook mode from the subscriber's loop circuit when the subscriber takes another telephone or other terminal equipment off-hook providing the subscriber instant access to the telephone without interference from the answering machine. This opportunity has not previously been available without first shutting off the answering machine manually.